4-Hydroxy Hexenal Derived from Docosahexaenoic Acid Protects Endothelial Cells via Nrf2 Activation

Abstract

Recent studies have proposed that n-3 polyunsaturated fatty acids (n-3 PUFAs) have direct antioxidant and anti-inflammatory effects in vascular tissue, explaining their cardioprotective effects. However, the molecular mechanisms are not yet fully understood. We tested whether n-3 PUFAs showed antioxidant activity through the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a master transcriptional factor for antioxidant genes. C57BL/6 or Nrf2−/− mice were fed a fish-oil diet for 3 weeks. Fish-oil diet significantly increased the expression of heme oxygenase-1 (HO-1), and endothelium-dependent vasodilation in the aorta of C57BL/6 mice, but not in the Nrf2−/− mice. Furthermore, we observed that 4-hydroxy hexenal (4-HHE), an end-product of n-3 PUFA peroxidation, was significantly increased in the aorta of C57BL/6 mice, accompanied by intra-aortic predominant increase in docosahexaenoic acid (DHA) rather than that in eicosapentaenoic acid (EPA). Human umbilical vein endothelial cells were incubated with DHA or EPA. We found that DHA, but not EPA, markedly increased intracellular 4-HHE, and nuclear expression and DNA binding of Nrf2. Both DHA and 4-HHE also increased the expressions of Nrf2 target genes including HO-1, and the siRNA of Nrf2 abolished these effects. Furthermore, DHA prevented oxidant-induced cellular damage or reactive oxygen species production, and these effects were disappeared by an HO-1 inhibitor or the siRNA of Nrf2. Thus, we found protective effects of DHA through Nrf2 activation in vascular tissue, accompanied by intra-vascular increases in 4-HHE, which may explain the mechanism of the cardioprotective effects of DHA.

Characterization of docosahexaenoic acid (DHA)-induced heme oxygenase-1 (HO-1) expression in human cancer cells: the importance of enhanced BTB and CNC homology 1 (Bach1) degradation

“…On the other hand, treatment of the EA.hy926 cell line with 100 μM DHA for various times dramatically enhanced Nrf2 nuclear protein expression (Figure 7C), consistent with a previous report [42]. DHA-induced Nrf2 nuclear translocation and HO-1 gene transcription was also reported in human umbilical vein endothelial cells (HUVEC) [43]. …”

Omega‐3 polyunsaturated fatty acids exert anti‐oxidant effects through the nuclear factor (erythroid‐derived 2)‐related factor 2 pathway in immortalized mouse Schwann cells

“…Furthermore, we identified the preventive effects of ω‐3 PUFAs against the oxidative stress‐induced cell death. The present findings are consistent with recent studies suggesting that the anti‐oxidant effects are induced by ω‐3 PUFAs in HUVECs and 3T3‐L1 adipocytes. ω‐3 PUFAs suppress inflammatory responses by inhibiting the arachidonate cascade in neutrophils, and the stimulation of the G protein‐coupled receptor 120 by DHA exerts anti‐inflammatory effects in macrophages.…”

“…ω‐3 PUFAs suppress inflammatory responses by inhibiting the arachidonate cascade in neutrophils, and the stimulation of the G protein‐coupled receptor 120 by DHA exerts anti‐inflammatory effects in macrophages. Recent studies report the anti‐oxidant effects of 4‐hydroxy‐2‐hexanal (4‐HHE), resolvin E1 and protectin D1, which are intracellular metabolites of ω‐3 PUFAs. We also examined the effects of 4‐HHE on the mRNA levels of anti‐oxidant enzymes and found that 4‐HHE increased the mRNA levels of Ho‐1 , Nqo‐1 and Cat (data not shown).…”

Omega-3 polyunsaturated fatty acids and oxygenated metabolism in atherothrombosis

“…Once oxidation reached a threshold level, the free radical chain reaction of lipid peroxidation might have exceeded the protection supplied by DHA, leading to pro-oxidant effects. In agreement with our results on 4-HHE, Ishikado et al[120] recently reported that supplementation with dietary fish oil led to increased HHE aortic concentrations and increased the expression of the antioxidant enzyme heme oxygenase-1, and endotheliumdependent vasodilatation. As reviewed very recently[121], potential molecular mechanisms to explain the antioxidant effects of omega-3 fatty acids would be the quenching of ROS as well as direct inhibition of NADPH oxidase 4 (Nox-4) by DHA[122].…”